Coupling arrangement for traveling wave tubes



Oct. 13, 1959 w. KLEIN ETAL 2,908,843

COUPLING ARRANGEMENT FOR TRAVELING WAVE TUBES Filed Au g. 22. 1955 INVENTCRS W KLEIN W FRIZ- G OSSWALD BY W1 United States Patent i COUPLING ARRANGEMENT FOR TRAVELING WAVE TUBES Application August 22, 1955, Serial No. 529,818

Claims priority, application Germany September 14, 1954 4 Claims. (Cl. 315-35) The focusing of electron beams in traveling wave tubes is effected mostly by means of permanent-magnetic or electromagnetic fields. To this end with electro-magnets 'the coils are arranged externally along the tube. For

coupling the HF-energy to the delay line, through coaxial lines the coil has to be interrupted at the coupling points. Arrangements have also already become known in which the HF-coupling is effected from one end of the tube. In such arrangements there is required no interruption of the magnet coil. However, the construction of the tube becomes very complicated because the coupling lines, at least partially, have to be conducted inside the vacuum container. In the case of waveguide couplings there is required, in most cases, an interruption of the magnet coil arrangement at the coupling points. When interrupting the coil arrangement then inhomogenities of the magnetic field must be taken into account. In the case of permanent magnets an interruption of the arrangement will lead to an intolerable drop of field intensity at the point of interruption. Especially in the case of low-noise traveling wave tubes a field inhomogenity causes an increase of the coil or helix loss current and, consequently, an increase of the noise factor.

For eliminating these disadvantages and for obtaining a field that is as free as possible from inhomogenities when employing electro-rnagnets as well as when employing permanent-magnets, the invention suggests a coupling arrangement consisting of a waveguide component and of a coaxial line component coaxially surrounding the tube. According to another feature of the invention the waveguide is arranged perpendicularly in relation to the tube axis, outside the homogeneous area of the magnetic field. The coaxial line component is arranged in the tube axis, i.e. in such a way that the tube can be accommodated in the inside of the inner conductor of the coaxial line section. The coupling between the coaxial line section and the tube is eifected at that end of the coaxial line section not facing the waveguide.

One exemplified embodiment of the invention will now be particularly described with reference to Figs. 1 and 2 of the accompanying drawing which represent a crosssectional longitudinal view of the tube and an end view, of the waveguide coupler, respectively.

In Fig. 1 the reference numeral 1 denotes the glass container of the schematically represented traveling wave tube, 2 denotes the beam generating system, 3 the input and output coupling arrangements of the tube, 4 is the collector comprising the heat radiating device 5. Numeral 7 denotes the input and output antennas for elfecting the transfer of the HF. energy between the outer circuits and helix 8, which is held in position between the holding bars 6. The inventive coupling arrangement includes a waveguide 9 equipped with the flange 10 that establishes the connection with the outer circuit. The tuning to the most optimum transformation plane is effected by means of the short-circuit slide 11. Perpendicularly to the waveguide there is arranged the inner conductor 12 of the coaxial line, and coaxially in rela- 2,908,843 Patented Oct. 13, 1959 tion thereto the outer conductor 13. As may be seen from the drawing, the input coupling arrangement is identical with the output coupling arrangement. The magnet arrangement 14 may consist of a one piece, coil or permanent magnet. When employing this arrangement it is possible to produce a magnetic field that is homogeneous over the whole length of the electron beam. The inner conductor 12 provides capacitive connection with the outer member of coupling arrangement 3. A similar connection is provided by the narrowed cylindrical portion of the outer conductor 13 of the coaxial line section and the other member of arrangement 3. The rela tionship between the diameter of the outer conductor and that of the inner conductor determines the characteristic impedance of the coam'al line section. It has to be matched to the waveguide, so that the dimensions of the coaxial line section depend upon the dimensions of the waveguide. For obtaining a good wideband matching it isregarded as being particularly advantageous to choose the distance between the inner and outer conductors of the coaxial line section to equal approximately the height 15 of the waveguide, that is the spacing between walls 16 and 17 of the waveguide.

For keeping the inner diameter of the magnet coil as small as possible it is appropriate to also keep the height a of the waveguide as small as possible. In this way there will result a small outer diameter of the coaxial line section.

What is claimed is:

1. In a traveling wave tube comprising an outer insulating envelope of predetermined diameter, a cathode gun at one end of said envelope, a collector electrode at the other end of said envelope, and a helical delay line extending along the length of said envelope substantially to said gun and said collector electrode, an energy transfer coupler for coupling an external circuit to said delay line, comprising a wave guide component substantially perpendicularly positioned with respect to said delay line and located beyond one end thereof, and a coaxial component external of and coaxial with said delay line and coupled to it at said one end, comprising an inner conductor member connected to one wall of said wave guide and extending toward said line, and an outer conductor member spaced axially from said inner conductor member and connected to the opposite wall of said wave guide and extending in coupling relation over one end of said line.

2. In a traveling wave tube according to claim 1, wherein said inner and outer conductor components are spaced radially from each other a distance substantially equal to the spacing between said wave guide walls.

3. The combination according to claim 2, further comprising capacitive coupling elements within the tube envelope for providing capacitive coupling with said inner and outer conductor members, respectively.

4. In a traveling wave tube according to claim 1, having a focusing coil for said traveling wave tube surrounding said envelope and extending beyond the ends of said delay line, the combination wherein said coupler is spaced beyond the end of said focusing coil.

References Cited in the file of this patent UNITED STATES PATENTS 2,578,434 Lindenblad Dec. 11, 1951 2,637,775 Lund May 5, 1953 2,730,649 Dewey Jan. 10, 1956 2,802,136 Lindenblad Aug. 6, 1957 2,809,321 Johnson et al. Oct. 8, 1957 2,836,758 Chodorow May 27, 1958 FOREIGN PATENTS 1,075,546 France Apr. 14, 1954 

